1. Field of the Invention
The present invention relates to an automatic focusing apparatus which drive-controls a photo-taking lens to make it pursue a moving object.
2. Related Background Art
There is known an automatic focusing apparatus which drive-controls a photo-taking lens to make it pursue a moving object. In the apparatus of this type a defocus amount of focus detection result is detected at a certain time interval for securing a charge storage time of sensor and a focus detection calculation time, and a moving speed of object is calculated based on current and past defocus amounts and the detection time interval between them. A drive amount of photo-taking lens is obtained by correcting the defocus amount with the thus calculated moving speed, and the calculated drive amount is set for a servo motor to drive-control the photo-taking lens.
In the conventional automatic focusing apparatus, however, the defocus amount and the moving speed of object are calculated at the time interval depending upon the charge storage time and the focus detection calculation time, and the drive amount is set for the servo motor in an intermittent manner. The intermittent input of drive amount causes a jerky motion of photo-taking lens, which in turn results in jerky movement of object image in a finder to raise a problem of bad feeling in use.
Especially, this phenomenon is outstanding in the so-called intermittent servo method in which the photo-taking lens is not driven during the charge storage in sensor. The motion of photo-taking lens is smoother in the so-called overlap servo method in which the photo-taking lens is driven also during the charge storage than in the intermittent servo method, because a newly calculated drive amount is reset during the drive of photo-taking lens. However, if a servo target becomes closer before a next drive amount is set, the servo motor is decelerated on occasion to assure the stop accuracy. Such deceleration also causes the jerky motion of photo-taking lens, raising the same problem as above.